The present invention relates to the fabrication of a magnetoresistive (MR) head and/or a giant MR head. More specifically, the present invention is a writer pole and a method of fabricating a writer pole for high density recording.
Thin film magnetic read/write heads are used for magnetically reading information from and writing information to a magnetic storage medium such as a magnetic disc or a magnetic tape. During a read operation, an MR reader (including a giant MR reader or a spin tunneling reader), consisting of various magnetic and nonmagnetic layers, is used to read magnetically encoded information from the magnetic medium by detecting magnetic flux stored on the magnetic medium. During a write operation, a writer, consisting of a top pole, a bottom pole, and a gap between the poles, writes information to the storage medium.
Bits of information are written to and stored on the storage medium in the form of a zero (0) or a one (1). During a write operation, the writer writes information to the storage medium by manipulating the polarity of the top and bottom poles to achieve the desired result. The polarity change in the writer head induces a change or transition in the stored magnetic field of the data storage medium.
It is desirable to provide a high density of information on the magnetic storage medium. Recording systems provide areal densities which are as high as possible for a given recording surface, within cost and fabrication limits. In the case of rotating disc drives (both floppy and hard disc), the areal density is found by multiplying the number of bits along a track by the number of tracks available per storage medium. The demand for increased storage density in magnetic storage media has led to reduced magnetic dimensions both in the area necessary to store information and in the apparatus used to read and write the information to the storage medium.
In order to provide the desired information density, the track widths of the storage medium are continually becoming smaller. Thus, it is desirable to fabricate a writer pole having a minimal width. High data storage density, such as 10 Gb/in2 and higher, will require a pole width narrower than 0.5 xcexcm. Currently, prior art writer poles are created by plating a pole material into a feature created by photolithographic techniques. However, the existing photolithographic techniques are limited to creating line widths of certain aspect ratios. The aspect ratio is defined as the depth of a hole divided by the width of a hole. With respect to the current photolithographic techniques for fabricating writer poles, the aspect ratio is the thickness of the photoresist, through which a hole is opened, divided by the width of the feature defined by the photoresist removed during the developing process. Thus, a hole having a depth of 20 xcexcm and a width of 5 xcexcm would have an aspect ratio of 20/5 or 4.
Fabrication of writer poles using prior art photolithographic and plating techniques is of limited utility for submicron poles, defined as having a pole width narrower than 0.5 xcexcm because of several process limitations inherent to photolithography and plating. The first limitation in creating submicron features is process capability limitations inherent to using photolithographic techniques. Applying prior art photolithographic technology to submicron features is limited because the process uses light having a wavelength longer than the width of the photoresist line to be printed. The width of the line printed in the photoresist effectively becomes the width of the writer pole. The smallest wavelength of light currently used in prior art applications is greater than 0.5 xcexcm, and as a result lines narrower than 0.5 xcexcm are difficult to fabricate within the tolerances required by submicron writer poles.
A second limitation to prior art photolithographic techniques are due to the physical limitations in the photolithographic process itself. Fabricating submicron features using a high aspect-ratio photoresist necessarily implicates fabricating a narrow cavity or hole in a thick photoresist. Since the exposure time necessary to process photoresist increases as the thickness of the photoresist increases, a thick photoresist requires a relatively longer process exposure time. As a result of the long exposure time, undesired inclined walls are formed in the developed cavity, where fabricating of a feature with non-inclined walls is desired.
Even if the limitations of the prior art photolithographic techniques were removed, the fabrication of submicron features in such a small opening would still be difficult because of physical limitations of the plating process utilized. Plating in small holes is difficult because of the surface tension of the plating solution fluid. Very small holes do not tend to get wetted by the solution. Wetting is a phenomena whereby a fluid is in intimate physical contact with a solid surface. Areas of the surface not wetted will not be plated because there is no way for ions in the plating solution to be deposited on the surface to be plated.
Even if the holes are somehow wetted, process control is still difficult because the plating solution in the holes is depleted of ions as ions from the plating solution are deposited onto the plated surface. In very small holes, such as those necessary to fabricate submicron features, the ions in the holes are not replenished because the ion replacement rate is limited by diffusion of the ions from the bulk fluid into the hole. The bulk concentration of the plating fluid is the concentration of the ions in the plating solution outside the volume of the holes and the bulk concentration is effectively a constant value because it is continuously mixed. The ion concentration in the hole is not a constant and varies with time since the ion replacement rate is diffusion limited because the plating solution in the holes is not well mixed with the plating solution in the bulk. As a result of the inhibited mixing between the plating solution in the holes and the plating solution in the bulk, the smaller holes are not uniformly plated. Thus, there is an uncontrolled process compared to when larger holes are plated, where the surface tension does not inhibit wetting of the surface and the ion concentration is more nearly constant due to the solution in the hole being replenished by turbulent fluid exchange with the bulk.
It is desirable to have a process of fabrication for submicron writer poles that allows for good process control and economical costs. Such a process would allow fabrication of varying writer track widths simply by changing the plating thickness rather than requiring a mask for each size. Since the plating process would be well characterized in such an application, the variation of pole width would be well controlled. While such a process would be useful in fabrication of submicron writer poles, any application requiring submicron features would benefit from such a process.
The present invention provides a writer pole having submicron features and a method of fabricating submicron features on a magnetoresistive head. In one preferred embodiment, the features created using the process of the current invention are submicron width writer poles. The process begins with a substrate material upon which a conductive seed layer is sputtered or deposited. A nonmagnetic feature is then plated onto the conductive seed layer.
One preferred method of fabricating the nonmagnetic feature would use the commonly employed steps of mask, expose, develop, and etch. First, after the conductive seed layer is placed on the substrate, photoresist would be applied to cover the entire conductive seed layer. The resist is then exposed so that when the photoresist is developed after exposure, a window is opened in the photoresist which exposes the seed layer where the magnetic feature is to be plated. The nonmagnetic feature is then plated on the exposed conductive seed layer in the window opening. After the nonmagnetic feature is plated in the open window, the remaining photoresist is removed.
After the resist is removed, the entire area containing the seed layer and nonmagnetic feature is masked, exposed and developed, whereby the area of the nonmagnetic feature where a pole will eventually be plated is opened and the remaining part of the nonmagnetic feature is covered with photoresist. The conductive seed layer adjacent to the area of the nonmagnetic feature to be plated is etched from the substrate. A writer pole is then plated on the portion of the nonmagnetic feature not covered with photoresist after the exposed photoresist is developed. The plated thickness of the writer pole on the nonmagnetic feature then becomes the width of the pole.